Motor drives are power conversion systems or “converters” that operate to provide power to electric motors in a controlled fashion to control one or more motor performance parameters, such as speed, torque, etc. Medium voltage current-sourced type motor drives typically receive multiphase AC input power in the range of about 2,400 to 6,900 volts, which is converted in a rectifier to DC power supplied to a DC link and provided from the DC link to an inverter. The inverter switches the DC link currents to provide AC output current to a motor load with the output current being controlled by the inverter in closed loop fashion to drive the motor at a desired speed and/or torque. The rectifier is generally an active switching type rectifier that selectively activates switches to provide current from the AC input to the DC link bus to achieve AC to DC power conversion, where the rectifier gain is controlled to provide a DC link current level at the peak current level required by the motor at any given time. The inverter, in turn, implements a switching scheme to selectively connect the motor leads to the DC link bus terminals to provide motor phase currents with controlled amplitudes, phase, and frequency to implement a particular motor control strategy based on motor performance feedback values and desired performance setpoints or profiles. Voltage source drives are similar but the DC link supplies a select constant DC voltage instead of a select constant DC current.
The rectifier and inverter switches are solid state devices such as, e.g., gate turnoff thyristors (GTOs), silicon controlled rectifiers (SCRs), insulated gate bipolar transistors (IGBTs), symmetrical gate commutated thyristors (SCGTs) or the like. Regardless of the exact type, these switches generate large amounts of heat that must be dissipated.
Commonly owned U.S. patent publication no. 2002/0089056A1 provides one example of such a motor drive, and the disclosure of said U.S. patent publication no. 2002/0089056A1 is hereby expressly incorporated into the present specification. U.S. patent publication no. 2002/0089056A1 discloses an air cooled motor drive wherein the switches of the rectifier and inverter are defined as “press-pack” switch devices mounted on respective printed circuit boards (PCBs). Each PCB includes a bracket adapted to be secured to a mounting location (such as a heat sink). When each PCB is operatively installed, the opposite terminals of its respective press-pack switch device are abutted with respective first and second heat sinks between which the PCB and switch are located for electrical and thermal conductivity between the heat sinks and the press-pack switch device, with electrical conductivity between the two heat sinks being controlled by the press-pack switch, itself. The heat sinks are electrically connected to power lugs which are, in turn, connected to power connectors for input or output of electrical power. The heat sinks are cooled by forced air flow generated by a fan or other source. For higher power applications, however, the heat sinks do not provide enough cooling. As such, a need has been found for such a motor drive with improved air cooling.